One known rotation transmission device which can selectively transmit rotation of a driving shaft to a driven shaft includes a two-way clutch and an electromagnetic clutch for selectively engaging and disengaging the two-way clutch.
The rotation transmission device disclosed in the below-identified Patent document 1 includes an outer ring, an inner ring mounted inside the outer ring, and a control retainer and a rotary retainer each having bars and mounted between the inner and outer rings such that the bars of the control retainer are arranged circumferentially alternating with the bars of the rotary retainer, whereby pockets are defined between circumferentially adjacent pairs of the bars of the respective retainers. The rotation transmission device further includes opposed pairs of rollers, each pair being mounted in one of the pockets, and elastic members each mounted in one of the pockets and biasing the opposed pair of rollers in the one of the pockets away from each other to a stand-by position where the rollers can instantly engage a cylindrical surface formed on the inner periphery of the outer ring and one of cam surfaces formed on the outer periphery of the inner ring such that when the inner ring rotates in either direction, one of each pair of rollers engages the cylindrical surface and the cam surface, thereby transmitting rotation of the inner ring to the outer ring.
The rotation transmission device further includes an electromagnetic clutch mounted on an input shaft, which carries the inner ring. The electromagnetic clutch is configured to move the control retainer in the axial direction when the electromagnet of the electromagnetic clutch is energized. When the control retainer is moved in the axial direction by the electromagnetic clutch, the retainers are rotated relative to each other in the direction in which the circumferential widths of the pockets decrease due to the action of a torque cam provided between the opposed surfaces of a flange of the control retainer and a flange of the rotary retainer, whereby the pairs of rollers are moved by the bars of the respective retainers to the disengaged position, thus preventing transmission of rotation from the inner ring to the outer ring.
In this rotation transmission device, when the electromagnet of the electromagnetic clutch is de-energized, the control retainer and the rotary retainer are rotated relative to each other in the direction in which the circumferential widths of the pockets increase under the biasing force of the elastic members mounted between the respective opposed pairs of rollers. Thus the rollers can instantly engage the cylindrical surface and the cam surfaces, so that the rollers scarcely move in the circumferential direction when engaging the cylindrical surface and the cam surfaces. The response time is thus short.